The present invention relates generally to automotive HVAC systems for controlling the environment of an automobile passenger compartment. More particularly, the invention relates to an air handling system for controlling the positioning of the fresh/recirc door in an automotive HVAC system.
This application is related to co-pending applications all filed on Nov. 12, 1998 and titled Refrigerant Flow Management Center For Automobiles, Reversible Air Conditioning And Heat Pump HVAC System For Electric Vehicles, Controller For Reversible Air Conditioning And Heat Pump HVAC System For Electric Vehicles, Anti-Fog Controller For Reversible Air Conditioning And Heat Pump HVAC System For Electric Vehicles, Controller For Heating In Reversible Air Conditioning And Heat Pump HVAC System For Electric Vehicles, and System For Cooling Electric Vehicle Batteries. Each of these applications is incorporated by reference into the present application.
Automotive heating ventilation and air conditioning, HVAC, systems have traditionally been single loop designs in which the full volume of refrigerant flows through each component in the system. In an HVAC system, refrigerant in the vapor phase is pressurized by a compressor or pump. The pressurized refrigerant flows through a condenser which is typically configured as a long serpentine coil. As refrigerant flows through the condenser heat energy stored in the refrigerant is radiated to the external environment resulting in the refrigerant transitioning to a liquid phase. The liquefied refrigerant flows from the condenser to an expansion valve located prior to an evaporator. As the liquid flows through the expansion valve it is converted from a high pressure, high temperature liquid to a low pressure, low temperature spray allowing it to absorb heat. The refrigerant flows through the evaporator absorbing heat from the air that is blown through the evaporator fins. When a sufficient amount of heat is absorbed the refrigerant transitions to the vapor phase. Any further heat that is absorbed raises the vaporized refrigerant into the superheated temperature range where the temperature of the refrigerant increases beyond the saturation temperature. The superheated refrigerant flows from the outlet of the evaporator to the compressor where the cycle repeats. Generally, the refrigerant flowing into the compressor should be in the vapor phase to maximize pumping efficiency. The operation of the refrigerant loop in conventional automotive HVAC systems is controlled by cycling the compressor on and off, and by varying the volume of refrigerant that is permitted to flow through the expansion valve. Increasing the volume of refrigerant that flows through the valve lengthens the distance traversed by the liquid before it changes to the vapor phase, allowing the heat exchanger to operate at maximum efficiency.
Advances in automotive HVAC systems have led to zone temperature control systems wherein different zones of an automobile are independently controlled. Zone control systems generally include an evaporator and expansion valve for each zone. The refrigerant flows through a compressor and condenser, then is split by a system of valves before flowing to the expansion valve and evaporator of each zone. The refrigerant flowing out of the evaporator of each zone is then recombined before returning to the compressor.
Further advances in automotive HVAC systems has led to the implementation of reversible heat pump systems in automobiles. In a reversible heat pump system the HVAC system can either heat or cool a compartment depending on the direction of the refrigerant flow. In the air conditioning mode refrigerant flows from the compressor through an outside coil (condenser) and into an expansion valve and inside coil (evaporator) before returning to the compressor. Heat energy is extracted from air that is blown through the inside coil (evaporator) into the passenger compartment thus providing cooled air. In the heating mode a four way valve reverses the flow of refrigerant through the coils, thereby reversing the function of the coils. Refrigerant flows from the compressor through the inside coil (condenser) then into an expansion valve and the outside coil (evaporator) before returning to the compressor. Heat energy in the liquefied refrigerant flowing through the inside coil is absorbed by air that is blown through the coil into the passenger compartment thus providing heated air. The air that is blown through the coil is a mixture of fresh outside air and air that is recirculated from the passenger compartment.
Generally, in conventional systems the precise mixture of fresh air to recirculated air is selected by the vehicle occupants. Permitting passengers to exercise absolute control over the air mixture selection normally enhances the comfort of the passengers. However, under some operating conditions it leads to reduced passenger comfort and less than optimal vehicle performance. For example, when a reversible HVAC system switches from air conditioning mode to heat pump mode fogging of the vehicle windows that occurs from moisture evaporating into the conditioned air is more likely if only recirculated air is flowing into the passenger compartment. Another example is air blow-by which occurs when a vehicle increases beyond a particular speed. When an intermediate air mixture setting is selected the increased air pressure from the speed of the vehicle causes air to flow back through the recirc ducts and out the inlets. The air exiting the inlets is unconditioned, directly subjecting passengers to outside air. Not providing automatic override of the air mixture setting can subject passengers to degraded operating conditions in which the solutions are not obvious to the passenger.
One object of the present invention is to provide a system for selectively overriding the passenger air mixture selection to enhance passenger comfort.
Another object of the present invention is to improve vehicle performance by automatically adjusting the air mixture during predetermined vehicle operating modes.
A further object of the present invention is to reduce the heat load on the HVAC system.
Accordingly, the invention provides an air-flow management system for controlling the supply air to a motor vehicle passenger compartment. The air-flow management system includes a reversible heat pump system for transferring heat energy between an outside environment and a refrigerant. Air from the outside environment, fresh air, and from the passenger compartment, recirculated air, is forced through the air-flow structure by a blower resulting in the transfer of heat energy between the refrigerant and the passenger compartment. A recirculation door provides a means for controlling the mixture of fresh air to recirculated air that flows through the air-flow structure. The position of the recirculation door is selectable by a controller to prevent fogging during the transition from cooling mode to heating mode, minimize the energy expended conditioning the passenger compartment air, and prevent the backflow of unconditioned outside air from the fresh air duct into the recirculation duct.
The above described device is only an example. Devices in accordance with the present invention may be implemented in a variety of ways.